Communication system



Sept, .18, 1945.l A. B. CLARK 2,385,061

i COMMUNICATION SYSTEM I Filed Jan. 1 -1945 5 Sheets-Sheet; l

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COMMUNICATION SYSTEM Fled Jn. l, 1943 45 Sheets-Sheet 2 A WS.

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A. B. CLARK A 2,385,061 GOMMUNICATIQN 'SYSTEM Filed Jan. l, 1943 s sheets-swat 4 /NvE/vroR v AacLAR/f y BK n WWW IY A T TORNEI sept. 11s, 1945. A, B. CLARK 2,385,061

COMMUNICATION SYSTEM Filed Jan. 1, 194s 5 sheets-sheet s /NVENTOR @y AB CLARK www@ ATTORNEY Patented Sept. 18, 1945 UNITED STATES PATENT'OFFICE COMMUNICATION SYSTEM'` Alva B. Clark, Maplewood, N. J., assignor toBell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application January 1, 1943, Serial No. 470,964

Claims. (Cl. 1797.1)

This invention relates to communication systems and particularly to systems in'which the subscribers are charged in accordance with the service rendered to them.

4 An object of the invention is to furnish telephone service at a relativelylow rate to subscribers Who make their calls during periods of light load and at a relatively high rate if their calls are made yduring periods of heavy load.

Another object of the invention is to furnish telephone service to a restricted class of subscribers ata relatively low rate during periods of light load and at a' relatively higher rate during periods of heavy load. v

Another object is to determine automatically Whether the oice is operating under a light load or a heavy load and to dispose of each call accordingly to facilitate the assessment of the appropriate charge therefor.

Another object is to apprise the subscriber at any time Whether he is entitled to make a call at the 10W or nominal rate he pays for his service or Whether the call if made will be charged at ahigher rate.

Another object is to make the lines of the restricted service subscribers available at all times forincorning calls from other subscribers Without regard to existing load conditions. l

Another object is to dispose of all -calls by restricted subscribers on the high-rate basis if made either during certain predetermined hours or periods of the day or at any time When the oice is heavily loaded and to dispose of such calls on the nominal or low-rate basis if made at any other time. "The invention in its broadest aspects contemplates a system in which a restricted service at a nominally low rate may be made available to the dilierent classes of subscribers lines, such as individual and party lines, lines of the flatrate class, and message register lines. It is particularly attractive from a cost standpoint when applied to party lines on a flat-rate restricted basis. The savings to be realized in the cost-of equipment and annular charges make it possible to oifer a service to this class of subscriberswhich entitles them, for a relatively loW nat-rate charge, to make an unlimited number of local calls, provided these calls are made when the oliice is operating under light load conditions, and whichk also entitles them to unrestricted service for incoming calls at all times. Moreover, these subscribers have the privilege of utilizing the facilities of the Oice at'all timesffor making calls in unlim-` ited numbers, subject to an additional charge for each call made when the ofce is operating under heavy load.

VA feature of the invention, therefore, is a system in Whichthe central ofce is provided with means for making continuous tests to determine the load condition of the office. The demarcation between light and heavy loads may be based on any oneV or on a combination of a number of conditions. In general, of course, it is chosen to mark the fact that the activity of the office has risen to a predetermined point' beyond which the ofce' is regarded as carrying a heavy load. In particular this transition from light to heavy load` can be indicated in terms of busy equipment units, such as line finders, trunks, senders, etc. 'Forexampla it is possible to measure the amount of current drawn by the operated control relays when a given number of line nders are in .concurrent use andato utilize this information inthe central oice controlling equipment to dispose of all calls thereafter from the restricted lines in such a .way that an additional charge is assessed against` the subscribers.

Another'feature isla system in which local calls by a restrictedV line during light oce load are completed in the usual manner Without incident, and inv which such calls, if made during heavy ,load periods, are automatically routed to an operator .who completes them and makes out tickets for assessment at a higher rate.

Another feature is a system of the character above described in which calls made during the heavy load periods are completed automatically by the calling subscribers and in which tickets are prepared automatically to record the higher rate of 'charge to be assessed against the ,subscribers.

A further feature of the invention is a system in'which the restricted service is applied to message register lines and in which the load condition'of the office is utilized to determine the appropriate vnumber of operations to be scored on the subscriber-s register for each call made.

A still further feature is the provision of means for apprising the subscriber, either in advance or whilehe isl in the act of calling, that the heavy load condition is prevailing and that the call he Wishes to make Will be charged at the higher rate. Theforegoing and other features of this invention will be described more fully in the following detailed' specification.

In"A thefdrawin'gs' accompanying this specification:

Figs. 1, 2 and 3, when taken together, illustrate a portion of an automatic telephone system incorporating the features of the invention.

Fig. 1 shows one of a number of subscribers lines and illustrates in conventional manner a line finder and first selector switch for establishing outgoing connections and selector and connector switches for setting up incoming connections;

Fig. 2 illustrates conventionally selector and connector switches for completing local calls to called subscribers lines and also illustrates an operators switchboard for assistance in completing these calls andfor establishing long distance connections; v

Fig. 3 shows a portion of the common Ipower equipment in the central office together with measuring and timing devices for determining the load condition of the office;

Fig. 4 is a detail view of the load-measuringy device;

Fig. 5 illustrates a modification of the system of Figs. 1, 2 and 3 in which automatic tickets are prepared for certain local calls and for long distance calls;

Fig. 6 illustrates a modification of the system to accommodate message register lines;

Fig. 7 shows an alternative arrangement for notifying the subscriber of the oilice load condition; and

Figs. 8, 9, and l0 show other alternative arrangements for apprising the subscriber of the load condition.

The present invention is applicable broadly to all types o communication systems such as .telephone and telegraph systems in which it may. be desirable to charge the individual subscribers Afor the service rendered in accordance with the load that is imposed upon the central office facilities. Itis particularly applicable to automatic telephone systems and may be applied to these without limitation with regard to` the types of switches and other controlling equipment used. For the purpose of .illustration the invention is disclosed herein embodied in an automatic telephone .system of the well-known step-by-step type. It is equally applicable, however, to systems of the panel and cross bar types in which register senders and markers are employed in the central ofce for controlling the switches to establish the desired connections,

AsA above mentioned, one of the important advantages of the present method of furnishing telephone service and assessing the charges therefor is the relatively low monthly rate that can be offered to subscribers who are willing in general to place their calls during periods when the central oice is lightly loaded. For a flat monthly rate the subscribers of this class are entitled to make an unlimited number of local calls during light loaded periods and are also entitled to make as many calls as they wish at any time subject, however, to being charged at a higher rate for every call made when the oiice is operating under heavy loading conditions. Furthermore, the subscribers of this restricted class areventitled to receive incoming calls from other subscribers at all times.

IThis service may also be given to subscribers of the message register class. All calls made by these subscribers during light load periods are scored by operating the calling subscribers message register a minimum number of counts for each call. However, if one of these restricted subscribers makes a call at a time when the oice is heavily loaded, the charge therefor is increased by automatically operating the message register a greater number of counts.

Referring to Figs. 1, 2 and 3 of the drawings, a subscribers line |00, which is assumed to be a flat-rate restricted service line, either of the individual or party line type, is shown appearing in the bank of the line finder switch F; and the line finder F is joined by a link circuit L with a rst selector switch S.

The selector switch S has a plurality of contact levels in its terminal bank, and some of these levels are preferably divided in two groups. For example, the level |0|, which serves to extend local calls, is divided into groups |02 and |03. The trunks |04 appearing in the group |02 extend to succeeding selector switches, such as switch S-|, which serve in conjunction with connector switch C to complete the local call to a called subscribers line 200. The trunks |05 appearing in the second group of contacts |03 extend to an operators switchboard 20| and the operators at this board, after receiving the necessaryinformation from the calling subscribers, complete the desired local connections over selectors S2 and connectors C-l to the called subscribers lines, such as the line 200. As will be explained hereinafter the brushes of the selector S, having been positioned opposite the level of the terminals |0| for a local call, are caused to hunt either in the first group |02 or in the second group |03 according to whether the ofce at the time is lightly loaded or heavily loaded.

l Other levels of the selector switch S, such as the level |06, are devoted entirely to trunks leading to the operators switchboard 20|. These trunks are chosen when the subscriber is dialing for a long distance call, and the operators at the board 20|` or at some other switchboard receive the necessary information from the subscribers and assist in establishing the desired toll calls. For a more detailed description of a switch of this type reference `is made to Wadsworth 2,249,067 of July 15, 1941.

The central office is also provided with a power or current supply equipment including the battery 300 and bus-bars 30| and 302. The load on the central oiiice at any particular moment, which will in general vary with the number of conversations taking place, may be determined by noting the extent to which certain equipment units are being used simultaneously. For example, the number of line iinders in operated position or the number of trunks in simultaneous use may be taken as a measure of the load on the office. In a system of the panel or cross bar type the num-ber of senders in simultaneous use is a fair indication of the extent to which the office is loaded. A convenient way of counting the number of equipment units in simultaneous use is to measure the amount of current drawn from the central oilice battery by these units. This may be accomplished by a current-measuring meter 303.

The meter 303 includes a sensitive needle 304, one end of which plays over the scale 305. The other end of the needle plays over Vthe metallic segments 306 and 301, which are insulated from each other, but normally does not touch either of them. Normally the needle does not touch either of these segments, but at regular intervals itwisltilted into circuit-making engagement with one or the other of these segments by means of a bail 308 of insulating material. The bail 308 is supported on the armatures 309 and 3I0 of electromagnets 3|I and 3|2, respectively. These magnets are energized repeatedly by an interrupter 3|3, and each time they energize the bail 308 moves the needle into engagement with either the segment 306 or segment 301, depending on the needle position, and holds it therevuntil the interrupter again opens. A side View of one of the bail-operating magnets is shown more clearly in Fig. 4.

The needle 304 is operated over the scale by an operating magnet 3I4, the energization of which is proportional to the current flowing in the circuit 3I5 from the battery bus-bars 30| and 302 to the operated line nders F--I, etc. Each finder that is in an operated condition has an energized relay supplied with current. over the common circuit 3|5. If, for example, nders F and F-I are busy, relay |01 in the finder F and relay |08 in the finder F-| are drawing current from the battery 300 over the circuit 3I5, and the voltage drop across the resistor 3|B causes the needle 304 to move to a position representative of the number of nders in operation.

As long as the central cnice is operated under a light load the needle 304 occupies some position above the metallic segment l30h. Each time the nterrupter 3|3 closes, the magnets 3II and 3|2 tilt the needle 304 into engagement with segment 306, and an obvious circuit is closed for operating the relay 3I1, although the relay 3I1 is without effect at this time. However, when the oice load reaches a predetermined point, the needle 304 passes beyond the segment 30B and over the segment 301 representing the heavy load. The next time the interrupterA 3|3 closes, the needle 304 is tilted onto segment 301, and a circuit is closed from battery through the winding of re-Y lay 3 I8, segment 301, needle 304 to ground. Relay 3|8 operates and locks through its armatureand contact to ground through the back Contact of relay 3l'1. Relay 3|8 remains locked as long as the oce is in a heavy load condition and serves, as will be explained hereinafter, to control the switching equipmentV in such la, manner that calls made by subscribers of the restricted class will be subject to charging at a higher rate. When the load on the office subsequently recedes below the predeterminedpoint, the needle 304 again passes over the segment 300; On the next closure of the interrupter 3|3, relay SI1-is operated to release the relay 3|8, thus restoringA the central ofce circuits to the flat-rate basis.V

In connection with this type of service it may be desirable to select certain fixed hours or other periods of the day and to `charge thevsubscribers of the restricted class on a higher rate for all calls made within these periods as well as for callsv which they make when the office is in its heavy load condition. This may be accomplished by any suitable clock mechanism 3|9. For example, if the hour from 9 until 10 in the morning is chosen as a busy hour, the clock mechanism 3|9 will close the contacts 320 during thisA period, thus operating the relay 3|8 without regard to the actual load on the oiice. When the busy hour passes, the clock 3| 9 reopens` the contacts 320, and the relay 3|8 isv now restored to the sole control of the load-measuring instrument 303.

In order that a party who has subscribed for this special. service may know at any time he is about to make a call whether the call Vvwill be covered by his flat monthly rate or whetheriit will be subject to an extra charge, his substation is equipped with some suitable signaling device. The subscribers line |00, for example, is equipped at the substation with a glow lamp which lights as a signal whenever the central ofce is heavily loaded. The subscriber, seeing the lighted lamp |09, knows that if he makes a call at such a time that he will be charged therefor at some predetermined rate. If, as hereinbefore noted, certain `predetermined hours or other periods of the day are designated as heavy load periodsvduring which all calls by special rate subscribers will be subject to extra charge, each Subscribers station in this class is also provided with a suitable schedule |I0 of the heavy load periods. For his regular lat monthly rate, therefore, a subscriber in this class is entitled to make an unlimited number of local calls, provided he makes them outside the hours or periods designated in the schedule ||0 and provided further that he does not call at anytime when the lamp |00 is lighted. Nevertheless, the facilities of the central oce are available to him at all times, and he may place as many calls as he wishes subject, of course, to the extra charge forcalls made when the office is in a heavy load condition.

The operation of the system illustrated in Figs. 1 to 3 will now be described. Assume first that the central oiiice is lightly loaded and that the subscriber of line |00 wishes to make a call to the subscriber of another line 200 in the local area. Since the oice is lightly loaded, the meter needle 304 is hovering somewhere above the segment 306, and relay 3|8 is in its released condition. With relay 3 I8 released, the relay I I I, which is common to the subscribers lines of the special class, is also in a released condition. When, therefore, the calling subscriber removes his receiver from the switchhook, a circuit is closed from the nega tive pole of battery ||2, which in reality is the same as` the central oilice battery 300, back contacts of the common relayV I II through the winding of the subscribers line relay I I3, normal contacts ofY cut-orf relay II4 thence over conductor I 26 of the subscribers line |00 and returning over conductor |28 to ground through the normal contacts of relay I I4. The current flowing in this circuit operates the line relay II3, but it should be noted that `the voltage of battery II 2 is not sufficient to light the lamp |09, notwithstanding the fact that the lamp is normally connected across the circuit including the battery. The line relay I I3 closes the usual line nder start circuit I I5, and the line nders, including the nder switch F, are set in operation to find the calling subscribers line |00. When the line has been found, the finder stops, and ground potential is applied to the sleeve conductor H6, causing the operation of the cut-oir relay I I4. Relay I I4 disconnects the line relay II3 from the tip and ring conductors of the calling line, and the start circuit |I5 is opened. lThe ground potential is also extended by way of the sleeve conductor II 1 of the line to render the line busy to incoming calls in the terminal banks of the connector switches The callingsubscriber now proceeds to manipulate his dial I I8 tooperate the selector switch S tion of an operator. 1 To this end the selector switch S, which is provided with two test brushes |20 and |2|, performs its automatic trunk hunting operation in the first group |02 of the selected level by testing the trunks of this group with its test brush |20, the test circuit extending through the normal contacts of relays |22 and |23 to a suitable test relay |24. When the rst idle trunk is found, such as the trunk H9, the connection is extended through to the succeeding selector switch S-I The calling subscriber continuing to maniplate his dial positions the selector S-l and the succeeding connector C to complete the connection to the desired subscribers line 200, Following the selection of the idle trunk ||9 relay |23 is operated, and a ground potential is returned in the Well-known manner over the sleeve conductor to operate the relay |25. .Relay |25 applies holding ground potential to the sleeve conductor ||6 to hold the line finder and cut-off relayduring the existence of the connection.

Aslong as the finder F is held in the connection thus established, the relay |01 is maintained in an energized condition by current flowing from the central office battery over the circuit 3|5. The voltage drop across the resistor 3|6 as a result of current flowing to the relay |01 is an indication that the nder F is engaged.

At the end of the conversation the subscribers replace their receivers, ground potential is removed from the holding conductors, relays |23, |25, |01 and ||4 release, and the switches are restored to their normal positions.

As the load on the oiiice increases, the number of finder switches F, F-|, etc. in concurrent use increases correspondingly, and the current drawn by the relays |01, |08, etc. increases the voltage drop across the resistor 3|6 until the needle 304 of the meter 303 passes beyond the light load segment 306 and over the heavy load segment 301. The next time the interrupter 3 |3 closes, a circuit is completed for operating relay 3|8, which locks tothe contactsof relay 3|1 and causes the operation of relay Relay disconnects the line relays of the lines in the special class from central ofce battery |2 and connects them through the resistor 322 to the relatively high voltage battery 323. If the special class of lines is large enough to warrant it, a plurality of relays similar to relay are provided, one for each of a group of lines of the special class, and these relays are all operated in parallel over the circuit closed at the inner right contact of relay 3|8. Relay 3|8 also applies ground potential to conductor 324, which has a multiple branch extending to each of the line nder selector links L serving the lines of the special class. The multiple branch |29 extending to the link L associated with finder F is connected to the armature of relay |25.. If the link L is idle at this time, the grounded branch circuit |29 is further eX'- tended through the winding of relay |30 to battery, causing the operation of relay |30, In like manner branch circuit |3| extends to the link including line finder F-I and causes the operation of the relay corresponding to relay |30 if the link is idle at the time. And the same is true of all other links serving the calls of the special service line. If, on the other hand, the link L is busy at the time relay |30 operates, relay |25 is in an energized condition,.and the application of ground potential to the conductor 324 does not cause the operation of relay |30. Similarly the 'relaysof all other busy links corresponding to relay |30 are unaffected.

Assume now that while the cnice is thus subjectedl to the heavy load condition the subscriber of line |00 desires to make a local call to the subscriber of line 200. At this time relay is energized as above explained, and a circuit is traceable from the high potential battery 323, resistance 322, front contacts of relay through the winding of line relay H3, contacts of cut-ofi relay ||4, conductor |26, resistor |21, lamp |09, conductor |28 to ground at the contacts of relay ||4. VThe voltage applied to the lamp |09 over this circuit causes it to glow, but the current flowing is insuiiicient to operate the line relay H3. Similar circuits are closed for the lamps on all other lines of this class which have their line relays connected in multiple to the armature of the common relay The subscriber of line |00, noting the glowing lamp |09, understands that the call, if made at this time, will be subject to an extra charge. If he decides, nevertheless, to proceed with the call, he removes his receiver whereupon a low resistance bridge is closed across conductors |26 and |28. This bridge short-circuits the lamp |09 to extinguish it and also permits suflicient current to flowthrough the resistance 322 to operate the line relay ||3. Relay ||3 closes the start circuit l5, and the finder F of an idle link is set in operation to find the calling line. When the nder reaches the calling line terminals, it stops, and ground potential is applied in the well-known manner to the sleeve conductor I6 to operate cut-off relay |4. Relay |4 releases line relay IIS, and relay |30, which is energized at this time over conductor 324, locks in a circuit from battery through its winding and front contacts to the grounded sleeve conductor ||6. When relay |30 operated, it closed an obvious circuit for the operation of relay |22, and the relay |22 shifts the test relay from its normal connection with the test brush |20 into connection with the alternative test brush |2| of the selector S. f

Since the calling subscriber wishes to converse with the subscriber of line 200 he manipulates his dial as before to position the brushes of` selector S opposite the level of terminals I0 Following the selection of the level |0| the switch S steps automatically in its trunk hunting movement over all sets of terminals in the group |02 regardless of their condition and tests the terminal sets in the second group |03 for an idle trunk |05 leading to the operators switchboard 2|) If the rst trunk |32 is idle at the time, the switch S selects it and extends the calling subscribers Line through to the answering jack 202 before an operator. As soon as'the switch S completes its trunk hunting operation relay |23 is operated in any suitable manner, and ground potential on the sleeve conductor is extended by way of brush |2| and the front contacts of relays |22 and |23 to the winding oi relay |25. Relay |25 operates to apply holding ground potential to the sleeve conductor I6 and to open the operating circuit of relay |30. Relay |30, however, remains locked to the grounded sleeve conductor. The operator answers the call with her cord circuit 203, asks the calling party for his number and also for the called subscribers number. She then connects her cord 203 to a trunk 204 and by means of a dial or key-set operates the selector S-2 and connector C to complete the connection to the called line 200. Having obtainedV this information from the calling subscriber and knowing that the call is subject to a charge, since it was routed to her over the trunk group |05, she makes out the necessary ticket from which the charge is subsequently applied to the subscribers monthly bill.

Inasmuch as the calls of the special class lines are routed to an operator when the oice is under heavy load the signal lamps at the subscribers stations may be dispensed with if desired. That is to say, the subscriber would make his call without knowing whether it was subject to the extra charge or not. If it were, the operator, on answering the call, would advise him of that fact, at which time he could elect either to continue with the call or to abandon it.

Since the tickets charging these calls tothe special rate subscribers are made out on the basis of oral information given to the operator at the time the calls are made, the usual number checking equipment may be provided if desired for verifying the calling line numbers given to the operator.

After the subscribers have finished conversing they `replace their receivers, the operator takes down her cord circuit 203, and the operated switches release to their normal positions. The removal of ground potential from the sleeve conductors causes the release of relays |25, 30 and |22. However, if the oice is still in a heavy load condition relay |30 is again operated over conductor 324, and relay |22 reoperates to prepare the link L for the next call.

Should the subscriber of line wish to make a toll or long distance call he may do so at any time Without regard to the load condition prevailing in the local oiiice. To obtain the long distance operator he initiates the call in the usual manner and dials a digit to position the brushes of switch S opposite the level of terminals |06 in which appear trunks |33 leading to a toll operators position at the switchboard 20|. In the level |06 the test terminals of all circuits in both groups |02 and |03 are arranged to be tested either over brush |20 or |2| for determini-ng their busy or idle condition. Therefore the switch S tests the trunks in this level as a single group and selects the first idle one therein. The operator at the board 20| answers the call with her cord 205, obtains the necessary information, makes out the appropriate ticket and extends the connection over the long distance circuit 206.

If desirable, all local calls made by the special class of lines may be completed on an automatic basis without the assistance of an. operator.V 'I'o this end the calls Iwhich fall within the flat-rate charge are completed as above described. However, all local calls made during the heayy load periods and all toll calls made at any time are completed on an automatic ticket basis. Referring to Fig. 5 for an understanding of this plan, the selector S-3, which corresponds to selector S in Fig. 1, is provided with divided levels, such as the level 500, having rst and second trunkv groups 50| and 502 therein. The trunks appearing in the first group 50| extend to selectors S-4 and conectors C-3 by means of which the calling subscriber completes his local calls unassisted when the ofce is under light load. When, however, the oflce is under heavy load, the switch S--3 hunts in the second group 502 on a local call and seizes an idle one of the trunks 503. Each of the trunks 503 is equipped with an automatic ticket printing mechanism y504--505 and terminates in local selector switches S-5. These local selectors have access through connectors C-I to the local subscribers lines, such as the line 506. When the calling subscriber dials for a long distance or toll connection, the switch S--3 hunts in the level 501 and chooses any idle one of the trunks 508 therein extending to the distant point. Each of the trunks 508 is also equipped with an automatic ticket printing mechanism 509-5|0.

It will be understood, of course, that the oice is also equipped with suitable means for determining the identity of the calling line whenever a connection is extended to one of the automatic ticket printing trunks, and this information is utilized for the purpose of controlling the ticket printing mechanism. For a better understanding of a system in which calling lines are identied and tickets are printed to charge the calls against the subscribers reference may be had to the application of J. W. Gooderham, Serial No. 448,782, filed June 27, 1942.

From theforegoing descriptions it will be understood that calls made by the special ilat rate subscribers may also be routed automatically Lto an operator or to an automatic ticket printing circuit during selected periods of the day. If, for example, it is decided that the hour from 9 to 10 in the morning is a busy hour period and justies a higher rate for subscribers of the special class, the .winding of relay 3|8 is connected to the clock operated contacts 320 in addition to its connection to the load measuring instrument 303. With this clock connection the contacts 320 close and remain closed from 9 until 10 oclock, and during this period the relay `3|8 remains continuously energized.

Although the lines of the special class are subject at times to extra charges, they are accessible for incoming `calls at all times and without any extra charge either to the special rate subscribers or to the subscribers making the incoming calls. These incoming calls are completed in the usual manner over the regular selector and connector switches S-G and C-2.

This special service may also be made available to subscribers lines of the message register class, if desirable. The general circuit arrangements for this purpose are illustrated in Fig. 6. The subscribers line 600 appears in the line lnder switch F2 which, together with selector S-'l and connector C--5, serves to extend the line 600 to called subscribers lines, such as the line 60|. Other lines of this class appear in the iinder F-2 and in the nnder F--3,a.nd the heavy load condition of the oil'ice may be determined by the number of relays 602, 603, simultaneously operated.

If the oflice is working under a light load at the time a call is made on the line 600, message register 604 of this line is operated a minimum number of times to charge for the call. However, if the office is under heavy load when the call is made, the circuits are automatically prepared to operate the register 604 at a higher rate or a higher number of times. 'As in Fig. 3, the load condition ofthe oilceis measured` by a meter, and a relay -505 'is operated whenever the ofiice is under a heavy load. Relay 605 operates the common relay 606 which disconnectsthe batis in a heavy load condition, relay 6|2 operates and, as will be explained later, shifts the message register operating 'circuitfrom the'slow interrupter S93 to the faster interruptor SI4. 'Similarly the grounded conductor SIO extends 'over lmultiple paths to all other idle links'to cause the operation of relays corresponding to relays SI2.

Assume now that the subscriber of line S00 makes a call while the office is in the light load condition. At this time relays S05, S06, SI2 and the corresponding relays in other links are deenergized. Since relay 60S is released the glow lamp SI5 is dark because the battery S01 is insucient to operate it. The subscriber knows, therefore, that the call he is about to make will ibe charged at the lower rate. When he removes his receiver, his line relay SIS operatesA in an obvious circuit, the line nder F-Z finds his line, and ground potential is applied to the sleeve conductor SI1 to operate the cut-oilv relay SIS. Relay SI8 releases the line relay BIS. The subscriber now operates his dial SIB to position the switches S-1 and C-5 to complete the connection to the called line SUI. Following the operation of switch S-1, relay 6I I operates and'opens the operating circuit of relay SI2, to prevent the latter from energizing in case ground potential is subsequently applied to conductor SID.`

At some convenient time relay 620 is operated to complete the message register operating circuit. This circuit may be traced from the positive pole of battery 62| through the slow interrupter SIS, conductor S22, back contacts of relay SI2, front contacts of relay S20, brush and contact of finder F-2 to the winding of message register S04 to the negative pole of battery. Under the control of the slow interrupter SIS the register S04 may be operated at a slow rate or a minimum number of times as desired.

Assume now that the oce is in a heavy load condition when the subscriber of line S00 initiates his call. The relay 'S06 being operated atthis time, a circuit is closed from the'battery S08, resistor 609, contacts of relay S06, winding of relay SIS, thence over the line through the glow lamp SI5 and over the other side of the line to .5

ground at the cut-off relay contacts. The subscriber sees the lamp glowing and knows that he will be charged at a higher rate. When he removes his receiver, the relay SIS operates to initiate the movement of the line finder F-Z, and the lamp SI5 is extinguished. As before, the subscriber manipulates his dial SI9 to operate the switches S-1 and C-5 to complete the connection. When switch S-1 is operated, relay 6II energizes and opens the operating circuit of relay SI2. Relay SI2, howeven'having been previously operated by the relay'005, remains energized in a locking circuit from battery through its winding and contact to the grounded sleeve conductor SI1. Subsequently when the relay 620 is operated, a message register operating circuit is closed through the fast interrupter SI15.' This circuit may be traced from the positive pole of battery 62|, interrupter SHI, conductor S23, front Vdiscs 800 and 83|.

calls are completed inthe usual manner overselector' switches and connector switches C-S.-

YIn the alternative signaling arrangement shown in Fig. 7 the subscribern determines the office load condition or the rate of charge enforced by listening to an audible tone in his receiver before initiating a call. If the office is lightly'loaded when the subscriber removes his receiver and iistens, a circuit is closed from battery through the back contacts of auxiliary relay 100, winding of line relay 10|, contacts of cut-off relay`12, conductor 103, condenser 10S, winding 105 ofthe induction coil, switchhook contacts, transmitter 106, dial 1&1, conductor 108 to ground at-l the contacts of relay 102. Because of the presence ci condenser 104 in this circuit relay 10i does not operate. The subscriber hearing no tone in his receiver knows that he is entitled to make a call for the lower or basic rate. On the other hand, if the oflice is heavily loaded, relay 1&3 is in an operated condition, and the circuit above traced extends through the front contacts of relay 100, winding of tone coil 109 to battery. As before, relay 10I does not operate because the condenser 104 is included in the circuit. Tone current does flow over the circuit, however, and the subscriber receives a characteristic toneA in his receiver, which serves as a signal to him that the call, if made, will be subject-to an extra charge.

If the subscriber, having removed'his receiver from the switchhook, decides to continue with the call, regardless of the ofce load condition, he operates the key 1I0. With the receiver switchhook in its alternate position the depressed key 110 locks to the displaced lever 1iI. The contacts of the key 1I0 close a short-circuit around condenser 104thus permitting'the line relay IUI to Operate. The relay 1E!! initiates the call in the manner already explained. At the end of the conversation the subscriber replaces the receiver on the switchhook and the lever 1i I permits the key 'H0 to restore to its normal position, removing the short-circuit from the condenser 104.

In the alternative form of the signaling arrangement shown in Fig. 8 the subscriber at the substation is apprised of the load condition or the rate of charge prevailing by means of a target ysignal showing either one of two colored If the oliice is lightly loaded, the auxiliary relay 802 at the central ollice is in its normal position, and current is supplied through the line relay 803 over the line loop in a given direction through the polarized target signal 80,4. When the subscriber removes his receiver, the circuit for the target signal is closed from the'negative pole of battery through the left normal contactsY of auxiliary relay 802, right winding of line relay 003, contacts of cut-cir relay 805, conductor B06 through the winding of -signal B04, winding 801 of the induction coil,

contacts of relay SI2, contacts of Yrelay S20 and ,4,35

thence through the message register B04. Under the control of interrupter SHI the register S04 is operated either at a faster rate or a higher number of times to charge the call against the subscriber.

As in the case of at-rate lines the message rate lines are entitled to receive all incoming calls made at any time without extra charge either to the message rate subscribers of the special class or to the calling subscribers.y These switchhook contacts, transmitter- 808, dial 808, conductor 310', contacts of relay 805, left-winding of relay 803, normal contacts of relay802 to ground. The polarized signal 804 operates its armature in one direction and exposes a particuvlar one of the colored targets 800 or 80| which signiiies the light load condition. The line relay 803 does not operate in series with the resistance of the signal winding 804. Therefore the removal of the receiver to determine the prevailing office load or rate of charge does not cause the unintended operation of a line finder switch in the central office. If, on the other hand, the oflice is heavily loaded or the higher rate of charge is in eiect, relay 802 is in its operated condition, and current ows over the line in the opposite direction causing the signal 804 to display the other colored disc which signifies the existing condition.

In either event, if the subscriber decides to continue with the call, he then operates the key 8| l. The key 8H is locked by the displaced lever 8i2 and at is closed contacts completes the shortcircuit around the signal device 804. The removal of the resistance of the signal winding 804 from the-circuit permits the line relay 803 to operate and initiate the call. When the subscriber later replaces his receiver on the switchhook, key 8H is restored, and the target signal 804 is again included in the circuit.

A further alternative is to provide a Voice-recording mechanism in the central oice which will give the subscriber an oral announcement when he undertakes to make a call while the office is heavily loaded or during one of the predetermined busy periods. This could be accomplished, for example, as shown in Fig. 9, by connecting the transformer 109 of Fig. 7 to a suitable voice reproducer. Another method, shown in Fig. 10, would be to connect one of the trunks 505 to a voice reproducer which would make the announcement as soon as the subscriber had dialed the first'digit.

As above explained, the features of the present invention are also applicable to automatic telephone systems of the type in which central oiiice register senders are used for controlling the switches. `Well-known systems of this type are those employing panel selector switches and cross bar selector switches. If the invention is incorporated in systems of this kind, the class information with respect to subscribers entitled to the special service is established in the register sender when the call is made by any of the well -known methods now in use. Also the load condition on the cnice may be communicated to the senders. With this information the sender is able to determine whether the call should be completed to the called subscribers line without incident or whether it should be treated specially by routing it to an operator or to an automatic ticketing circuit.

For the purpose of illustrating the principles of the invention applicant has described it with particular reference to subscribers lines of the flat-rate and message-rate classes. It will be understood, however, that it applies to all classes of lines and that it contemplates the extension of the special service to al1 subscribers of an oflice.

The central cnice batteries 300 and 630 furnish current for the talking connections and also for operating the various controlling relays. For simplicity of illustration the battery is shown conventionally in a number of different locations throughout the drawings, but it will be understood that this method of illustration is used merely to facilitate an understanding of the circuit operation. It may be also noted that batteries 323, G08 and 62| are special sources for operating the signal lamps at the subscribers stations and for operating the message registers.

What is claimed is:

1. The combination in a telephone system of a central telephone oice, subscribers lines terminating in said oce, means for establishing conversational connections between said lines, means for measuring the load on said office, the operation of said measuring means bearing a predetermined relation to the total number of conversational connections concurrently established, and means controlled by said load measuring means for determining the rate of charge to be made against said subscribers.

2. The combination in a telephone system of a central telephone ofce, subscribers lines terminating in said oilice, means for establishing conversational connections between said lines, measuring means for determining Whether said oiice is operating under a light load or a heavy load, the operation of said measuringmeans bearing a predetermined relation to the total number of connections concurrently established, and means controlled by said load measuring means for determining whether the subscribers are to be charged at a relatively low rate or at a relatively high rate.

3. The combination in a telephone system of a central telephone oliice, subscribers lines terminating in said oce, means for-establishing conversational connections between said lines, measuring means for determining whether said oiice is operating under a light load or a heavy load, the operation of said measuring means bearing a predetermined relation to the total number of connections concurrently established, means for appraising a subscriber of said load condition at the time he wishes to make a call, and means controlled by said load measuring means for determining whether the subscriber shall be charged at a relatively low rate or at a relatively high rate.

4. The combination in a communication system of a central office, subscribers lines terminating in said central office, means for establishing a variable number of concurrent communication connections between subscribers lines, variably operable means for measuring the load on said oiiice, the operation of said measuring means at any given time bearing a predetermined relation to the total number of concurrent connections then established, and means controlled by said load measuring means for determining the rate of charge to be made against said subscribers. f

5. The combination in a telephone system of a central telephone olce, subscribers lines terminating in said cnice, equipment units in said ofce for setting up conversational connections between said lines, variably operable means for measuring the load on said ofce, the operation of said measuring means being proportional to the total number of equipment units in simultaneous use at any particular time, and means controlled by said load measuring means for changing the rate of charge made against said subscribers.

6. The combination in a communication system of a central ofce, subscribers lines terminating" in said oice, switching units in said oiice for establishing communication connections between said lines, a source for supplying current to all switching units in use, variably operable means for measuring the load on said ollice, the operation of said measuring means being proportional to the current supplied from said source to the engaged switching units, and means controlled by said measuring means for changing the rate of charge made against said subscribers.

7. The combination in a communication system of a central oiice, subscribers lines terminating in said cnice, controlling units in said oice for controlling the establishment of communication connections between said lines, a source for supplying current to said controlling units, variably operable means for measuring the load on said oihce, the operation of said measuring means being proportional at all times to the total current supplied to said controlling units, and means controlled by said measuring means' for varying the rate of charge in accordance with the lar time for selecting the rate of charge, and means for apprising a subscriber making a call of the prevailing rate of charge.

9. The combination in a measured service telephone system of a central telephone office, subscribers lines terminating in said oiiice, switching means in said oilce for setting up conversational connections between said lines, means for chargine a subscriber at any one of a plurality of diiferent rates, means dependent on the number ci' concurrent conversations at any particular time for selecting the rate of charge, and signal means at each subscribers station for apprising him of the rate at which he will be charged in the event he makes a call.

l0. The combinationin a telephone system of a central telephone oilce, subscribers lines terminating in said oflice, equipment units in said cnice for setting up conversational connections between said lines, measuring means variably operated in accordance with the number of equipment-l units in simultaneous use at any particular time for measuring the load on said oce, means for charging the subscribers at different rates dependent on the cnice load, and signal means controlled by said load measuring means for apprising ansr subscriber of the rate at which he is being charged.

11. The combination in a measured service telephone system of a central telephone oilce, subscribers lines terminating in said cnice, switching means in said oice for setting up conversational connections betweenfsaid lines, measuring means variably operated in accordance with the number of simultaneous conversations taking place at any particular time for measuring the load on said oice, means for charging the subscribers at any one of a plurality of different rates, means controlled by said load measuring means for selecting the rate of charge, and means controlled by said load measuring means for apprising any subscriber of the prevailing rate of charge.

12. The combination in a measured service telephone system of a central telephone cnice, subscribers lines terminating in said cnice, Switching means in said oice for setting up conversational connections between said lines, means foi charging a subscriber at any one 0f a plurality of diierent rates, means dependent on the number of concurrent conversations at any particular time for selecting the rate of charge, signal means at each subscribers station and operable over his line from the central ofce for indicating to him the rate of charge prevailing at any time, means controlled by the subscriber for rendering said signal means effective without initiating a call in the central ofce, and means controlled by the subscriber for disabling said signal means and for initiating a call over his line after he has been apprised of the prevailing rate of charge.

13. The combination in a telephone system in which a subscriber is charged at a low rate for calls made when the oice is lightly loaded, of means for determining the oice load condition, means under the sole control of said subscriber for completing a call when the cince is lightly loaded, an operators position, means effective when the oice is heavily loaded for routing said subscribers call automatically to said operator who answersit and prepares a ticket charging the subscriber at a higher rate, and means controlled by the operator for completing said subscribers call.

14. The combination in a telephone system in which a subscriber is charged at a low rate for calls made when the oice is lightly loaded, of means for determining the cnice load condition, means for completing under'the sole control of the subscriber all calls made during both light and heavy load periods, and means effective when the office is heavily loaded for preparing tickets automatically to charge the subscribers at a higher rate for each call.

l5. The combination in a telphone system in which a subscriber is charged at a low rate for calls made when the olice is lightly loaded, of means for determining the ofce load condition means for completing under the control of the calling subscribers local calls and toll calls made during either light or heavy load periods, means effective when the office is heavy loaded for preparing tickets automatically to charge the sub scribers at a higher rate for all local calls, and means effective without regard to the load condil tion o the office for preparing tickets automatically to charge the subscribers at predetermined rates for all toll calls.

ALVA B. CLARK. 

